From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ricardo Wurmus <rekado@elephly.net>
Subject: Re: nesting with-imported-modules
Date: Thu, 20 Feb 2020 10:01:05 +0100
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To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Cc: guix-devel@gnu.org


Ludovic Court=C3=A8s <ludo@gnu.org> writes:

> Hello!
>
> Ricardo Wurmus <rekado@elephly.net> skribis:
>
>> it seems that it is impossible to nest with-imported-modules.  A gexp
>> that is wrapped in multiple layers of with-imported-modules won=E2=80=99=
t depend
>> on the list of all mentioned modules but only on the outermost.
>>
>> This is because with-imported-modules sets the current-imported-modules
>> parameter without checking if the parameter already has a value.
>>
>> Should nesting be supported?  It seems useful.
>
> Is it?  :-)
>
> My impression is that one would always write:
>
>   (with-imported-modules =E2=80=A6 #~(=E2=80=A6))
>
> or possibly combining multiple expressions:
>
>   (define e1 (with-imported-modules =E2=80=A6 #~(=E2=80=A6)))
>   (define e2 (with-imported-modules =E2=80=A6 #~(=E2=80=A6 #$e1 =E2=80=A6=
)))
>
> in which case modules are appended.
>
> I couldn=E2=80=99t think of a use case where one would literally write:
>
>   (with-imported-modules =E2=80=A6
>     (with-imported-modules =E2=80=A6
>       #~(=E2=80=A6)))


No, I=E2=80=99m not writing this literally, but I have an expression that u=
ses
(guix search-paths), for example.  Then I have another procedure that
takes this expression and wraps it with an expression that uses (gnu
build linux-container).

--8<---------------cut here---------------start------------->8---
(define (containerize exp)
  (with-imported-modules (=E2=80=A6 (gnu build linux-container) =E2=80=A6)
    #~(begin
        (use-modules (gnu build linux-container))
        =E2=80=A6
        #$exp)))

(define (generate-exp)
  (define exp
    (with-imported-modules (=E2=80=A6 (guix search-paths) =E2=80=A6)
      #~(begin
          (use-modules (guix search-paths))
          =E2=80=A6)))
   (if container? (containerize exp) exp))
--8<---------------cut here---------------end--------------->8---

The observed effect was that only one of the with-imported-modules calls
had any effect on the final expression.

--
Ricardo